Optimised method for curing tyres and related device for its achievement

ABSTRACT

A method for curing a tire includes the steps of closing the tire in a mold, heating at least one lower hot table, at least one upper hot table, and at least one annular hot table to transmit heat to the tire. The at least one lower hot table, the at least one upper hot table, and the at least one annular hot table are associated with the mold. The at least one annular hot table is thermally-connected to a circumferential development of the mold. A quantity of heat provided to the at least one lower hot table is different from a quantity of heat provided to the at least one upper hot table. An associated apparatus includes a mold; at least one lower, upper, and annular tables; and devices for supplying one or more heating fluids to the at least one lower, upper, and annular tables.

[0001] The present invention relates to a method for curing tires,comprising the phases of closing a tire to be cured in the moulding andcuring cavity of an appropriate mould and of heating the lower, upperand lateral walls of said mould to transmit heat to the tire

[0002] The invention further relates to a device for curing tires,comprising: a curing mould defining a moulding and curing cavitysuitable to receive a tire being processed at least a lower hot tablesituated adjacently to a lower wall of said curing mould; at least anupper hot table situated adjacently to an upper wall of said curingmould, at least a peripheral hot table situated around the lateraldevelopment of the moulding and curing cavity; devices for supplyingheating fluid in said hot tables.

[0003] Production processes for vehicle tires provide for each tire,after having been assembled in all its components, to be subjected to amoulding and curing process during which the tire itself is made toadhere with adequate pressure against the inner walls of a mouldingcavity, and to the administration of heat to determine, with thepolymerisation of the elastomeric material whereof it is composed, itsdefinitive geometric and structural stabilisation.

[0004] With particular reference to the curing of tires for vehicles,for this purpose the use of so-called centripetal devices is widespread.Examples of such devices are for instance described in the followingpatents: U.S. Pat. No. 5,676,980, EP 123,733, EP 170,109 and EP 459,375.

[0005] Devices of this kind are generally arranged with the axis of themould in vertical position and the median, or equatorial plane, of themould horizontal relative to the ground; the moulding cavity isessentially defined between two annular cheeks, respectively inferiorand superior with reference to said plane, coaxially arranged to formthe exterior surfaces of the sidewalls of the tire. To the cheeks iscombined a crown of sectors arranged circumferentially around thegeometric axis of the mould, coinciding with the axis of rotation of thetire, to shape the tread band of the tire, define therein a series ofindentations and/or grooves arranged in varied ways according to adesired tread design.

[0006] The lower cheek is generally fixed relative to a base, whereasthe upper cheek, engaged to a so-called lid movable vertically, can betranslated axially relative to the lower cheek.

[0007] The circumferential sectors, in turn, are slidingly engaged to asector-holder ring which is integral, depending on the case, either withthe lid or with the base. More in particular, the sectors are movablealong respective generatrices of a cone frustum shaped surface providedin the sector-holder ring. Simultaneously with the mutual axialactuation between ring and sectors, the latter are simultaneouslytranslated radially to the axis of the mould, between an open conditionwherein they are circumferentially distanced from each other, i.e.radially removed from the outer circumferential surface of the tirecontained in the mould, and a closed condition wherein they are radiallyapproached and mutually matching in correspondence with the respectivecircumferentially opposite edges.

[0008] Hearing devices are further provided for transmitting apre-determined quantity of heat to the tire closed in the mouldingcavity, in order to determine its adequate curing.

[0009] These heating devices essentially comprise a plurality ofso-called “hot tables” positioned around the components that define themoulding and curing cavity. For the purposes of the present description,the term “hot table” is taken to mean a structural part of the curingunit, presenting at least a cavity, different from the moulding andcuring cavity, able to be supplied with any suitable heating fluid.

[0010] More specifically, a lower hot table, located immediatelyunderneath the aforesaid lower cheek, an upper hot table, locatedadjacently above the upper cheek, and an annular hot table associatedwith the sector-holder ring and extending around the sectors themselves,are provided.

[0011] Whilst the upper and lower hot tables are supplied with fluid,usually steam, at the same temperature, in the order of 175° C. by wayof indication, the fluid injected into the annular hot table can have atemperature in the order of 185° C., or in any case exceeding thetemperature of the fluid injected into the lower and upper chambers.

[0012] This greater temperature is selected in consideration of the factthat the crown of the tire, in contact with the sectors, has a greaterthickness than the thickness of the sidewalls and includes the beltstructure, i.e. a pack of at least three strips of rubber-coated fabric,textile or metallic, and thus requires a greater quantity of heat toreach, in the same cycle time, substantially the same degree of curing.

[0013] In particular, it is also known document GB 1,118,005 disclosingan apparatus for embossing a pattern in the tread band of a pneumatictire of the type described above which may supply steam at differenttemperatures to the chambers of the hot tables in dependence of thethickness of the parts of the tire to be cured.

[0014] It has always been deemed that the known curing method describedabove allowed to fabricate tires with a homogeneous degree of curing or,at least, with any inconsistencies symmetrically distributed relative tothe equatorial plane in relation to the different thickness between thedifferent areas of the tire and to the different size of the carcass insaid areas.

[0015] After the premise above, it should be noted that the tireindustry constantly strives to search for continuous improvements bothof the performance offered by the tire in operation and of the degree ofuniformity of the product in order continually to restrict the band oftolerability of the values of the viscosity and elasticitycharacteristics of the cured tire which deviate from the pre-determinedideal value.

[0016] In this search for continuous improvements, sustained by anaccurate analysis of the product, the Applicant has found that the tireoften behaves differently , to a greater or lesser extent, when engagedin a curve in a given direction from the way it does when engaged in theopposite direction.

[0017] This inconsistent behaviour was initially and hastily attributedto tolerable quantitative differences between the geometriccharacteristics (thickness, height and profile) of the two semi-finishedproducts that constituted the opposite sidewalls of the tire or to smallvariations in the geometric characteristics of the compound of the twosidewalls which took place during the sidewall preparation (straining orcalendering) process.

[0018] However, as manufacturing processes and process control systemsimproved, this notion no longer seemed convincing: the Applicant thusintuited that perhaps the two sidewalls of the tire, while having thesame chemical composition, and specifically the same quantity of thedifferent ingredients in the formula of the compound, as well as thesame geometric dimensions, could yet present some diversity in thephysical and or viscous-elastic properties of the compound, notperceivable at first glance, caused by or in any phase of the tiremanufacturing process.

[0019] The Applicant found that tires with the aforesaid inconsistentbehaviour in curves presented sidewalls mainly with a different value ofthe elasticity module and intuited that such difference in value was tobe linked to a different degree of curing of the sidewall compound. TheApplicant then understood that the known curing method, with the intentof obtaining a tire with homogeneous characteristics, in particular withregard to the sidewalls, had transferred the concept of homogeneity alsoto the temperatures whereas the steam was supplied to the hot tables ofthe curing mould.

[0020] In practice, instead, also for the specific lay of the curingmould with the cheeks radially superposed and parallel relative to theground, the imposition of a homogeneous supply temperature for the twotables, lower and upper, did not translate into a homogeneous quantityof heat absorbed by the sidewalls of the tire

[0021] Indeed, the equality of the temperatures of the steam introducedinto the lower and upper hot tables, led in fact to a non-homogeneousthermal condition of such tables since the lower hot table, transmittingand irradiating heat upwards, contributed to heating the upper hot tablewith the consequent greater heat absorption thereby.

[0022] This different heat absorption by the two hot tables, and by thecorresponding cheeks of the mould, entailed a different quantity of heattransferred to the sidewalls of the tire and hence a different degree ofreticulation between the two sidewalls, with the consequent diversity inmechanical and behavioural characteristics observed in the finished tire

[0023] In accordance with the invention, the problem has been solvedwith a different heating of the two hot tables, lower and upper,dimensioned taking into account the transmission of heat between thedifferent parts of the curing device, in order to determine an equalabsorption of heat by the two sidewalls subjected to curing It wasfurther noted that this way of proceeding allows also to improve thecuring homogeneity of the circumferential portions of tread on theshoulders of the tire.

[0024] In a first aspect, the invention thus relates to a method forcuring a tire entailing the use of curing mould presenting a mouldingand curing cavity suitable for receiving a tire being processed, a lowerhot table and an upper hot table axially opposed and suitable foroperating on respective sidewalls of the tire and at least an annularhot table positioned around the circumferential development of themoulding and curing cavity, comprising the following phases:

[0025] closing a tire to be cured in said moulding and curing cavity;

[0026] heating the lower, upper and annular hot tables to transmit heatto the tire, wherein different quantities of heat are transferred tosaid hot tables during said heating phase, in order to cure the tirehomogeneously.

[0027] In accordance with a first aspect of the present invention, itwas found that it is possible to achieve unexpected improvements in thetire curing process, particularly in terms of homogeneity in the entirestructure of the cured tire, if the hot tables, or different portionsthereof, are supplied independently with different heat inflows, and inparticular if the temperature of the steam or other heating fluid fedinto the lower hot table is higher than the temperature of the heatingfluid fed into the upper hot table.

[0028] In accordance with this aspect of the invention, a method forcuring a tire is characterised in that the tire heating phase is carriedout supplying the lower hot table with heat in a greater quantity thanthe heat supplied to the upper hot table.

[0029] Alternatively or in combination with this aspect, also theheating of the annular hot table is performed by supplying its lowerportion with heat in greater quantity than the heat supplied to itsupper portion.

[0030] Preferably, the heating of the hot tables is effected bysupplying a heating fluid to the hot tables themselves, and still morepreferably, the fluid supplied to the lower hot table and/or to a lowerportion of the annular hot table has a greater temperature than thetemperature of the fluid supplied to the upper hot table and/orrespectively to an upper portion of the annular hot table itself.

[0031] For this purpose, the fluid supplied to the lower hot table canadvantageously also be supplied to a lower portion of the annular hottable, whilst the fluid supplied to the upper hot table canadvantageously also be supplied to an upper portion of the annular hottable.

[0032] According to a preferential embodiment, the fluid supplied to thelower hot table comprises dry saturated steam at a temperature rangingbetween 155° C. and 165° C., whilst the fluid supplied to the upper hottable comprises dry saturated steam at a temperature ranging between148° C. and 158° C.

[0033] In one of its different aspects, the invention relates to adevice for curing tires for wheels of vehicles, wherein the devices forsupplying the fluid supply differentiated portions of said hot tables inmutually independent fashion, and in particular, they supply the lowerhot table with fluid at higher temperature, than the temperature of thefluid supplied to the upper hot table.

[0034] Preferably, the annular hot table is divided into at least alower cavity and at least an upper cavity according to a diametricalplane relative to the moulding and curing cavity, so that the fluidsupplying devices can supply the lower cavity of the annular hot tablewith fluid at different, preferably higher, temperature, than that ofthe fluid supplied to the upper cavity of the annular hot table itself.

[0035] For this purpose it can preferably be provided for the lowercavity of the annular hot table to be in fluid communication with thelower hot table, whilst the upper cavity of the annular hot table is influid communication with the upper hot table.

[0036] According to a preferential embodiment of the invention the fluidsupplying devices further comprise at least an injection conduitdischarging into the interior of the moulding and curing cavity and atleast an extraction conduit originating from the same moulding andcuring cavity.

[0037] In accordance with a different preferential embodiment of theinvention, the lower cavity and the upper cavity of the annular hottable are respectively obtained in an upper containment portion and alower containment portion of a containment structure; preferably, saidcontainment portions are mutually movable between a closed conditionwherein they are in mutual contact, mutually matching preferably on adiametrical plane of the moulding cavity, and an open condition whereinthey are mutually axially distanced.

[0038] More in particular, in the closed condition the upper containmentportion and the lower containment portion can advantageously mutuallymatch according to a median equatorial plane of the moulding and curingcavity.

[0039] In accordance with a further aspect of the invention, which canalso be exploited independently of the above description, the mouldcomprises the usual crown of sectors divided into a plurality of lowerradial sectors and a plurality of upper radial sectors respectivelyengaged in said lower and upper containment portions, circumferentiallydistributed around the geometric axis of said moulding and curingcavity; each of said sectors comprises a support body slidingly engagedin the corresponding containment portion to be selectively moved,simultaneously with the mutual axial motion of the containment portions,between a closed condition, wherein said sectors are mutually approachedand matching to define the moulding and curing cavity, and an opencondition wherein the sectors of the same plurality are radially removedrelative to the aforesaid geometric axis, circumferentially distancedfrom each other, and axially distanced relative to the sectors of theopposite plurality, and each of said sectors further comprises at leasta moulding die removably engaged to the support body.

[0040] Preferably, in the closed condition the lower sectors and theupper sectors mutually match according to the equatorial median plane ofthe moulding and curing cavity.

[0041] It is also preferable for each of said sectors to be operativelyengaged in the annular containment portion, slidingly guided along acorresponding cone frustum shaped surface obtained on the inner surfaceof its containment portion, respectively lower and upper, to determinethe mutual radial removal of said sectors.

[0042] Preferably, to each support body are engaged at least two of saidmoulding dies able to slide on the support body itself and mutuallymovable according to a circumferential direction relative to themoulding and curing cavity.

[0043] Each of said moulding dies advantageously presents acircumferential extension corresponding to at least a pitch of a treaddesign to be defined on the tire being manufactured.

[0044] In accordance with this inventive aspect of the subject device,the curing cycle of the tire, once the curing phase has been completed,comprises the additional phase of removing the dies from the aforesaidgeometric axis, to open the curing mould, guiding said dies by means ofindentations produced by the dies themselves in the tread band.

[0045] Further features and advantages shall become more readilyapparent from the detailed description of a preferred but not exclusiveembodiment of a method and a device for curing tires for vehicle wheelsaccording to the present invention.

[0046] The description shall be given below with reference to theaccompanying drawings, provided purely by way of non-limitingindication, in which:

[0047]FIG. 1 is a diametrical section of a device according to theinvention, with a tire undergoing work closed in the moulding cavity;

[0048]FIG. 2 shows a semi-section of the device of FIG. 1 in anoperative phase in which circumferential sectors of the curing moulddisengage the tire undergoing work;

[0049]FIG. 3 shows a semi-section of the device in an operative phase inwhich the detachment of tire from the upper cheek of the curing mould iscarried out;

[0050]FIG. 4 shows a semi-section of the device in an operative phase inwhich the tire is extracted from the lower portion of the mould;

[0051]FIG. 5 shows a phase whereby the tire is laid onto a support planewith rollers;

[0052]FIG. 6 is an interrupted section taken according to the traceVI-VI of FIG. 2

[0053] With reference to the aforementioned drawings, the referencenumber 1 indicates in its entirety a device for curing tires for vehiclewheels, according to the present invention.

[0054] The device 1 comprises a curing mould 2 operatively housed in acontainment structure 3 and defining in its interior a moulding andcuring cavity 4 suitable to receive a tire 5 undergoing work.

[0055] More in particular, the mould 2 essentially presents a lowercheek 6 and an upper cheek 7 mutually coaxial and able to operate onrespective sidewalls 5 a of the tire 5, as well as a crown of radialsectors 8 circumferentially distributed around a geometric axis Y-Y ofthe moulding cavity 4, coinciding with the axis of rotation of the tire5, and able to operate on a tread band 5 b of the tire itself.

[0056] Within the moulding cavity, a curing bag of the usual kind (notshown) can operate, but in the preferential embodiment of the inventionit is preferred to omit such a bag which constitutes a disadvantageousobstacle to the transmission of heat towards the radially interiorsurface of the tire.

[0057] For the purpose of locking the position of the tire undergoingwork within the moulding cavity, an upper gripping organ 30 and a lowergripping organ 31 are preferably associated to the lower cheek 6 andupper cheek 7, the gripping organs 30 and 31 can be activatedindependently of each other in any convenient way, to be brought from aresting position wherein their diametrical size is lesser than the innerdiameter of the bead of the tire 5, to an operative condition whereinthey present a greater diametrical size than said diameter so that theyare able to hold respective beads 5 c of the tire 5 in correspondencewith the inner circumferential edges of the respective lower cheek 6 andupper cheek 7.

[0058] Alternatively, the tire undergoing work can be mounted on a rigidsupport (not shown) having the shape of the inner surface of the tire,whereon the tire has preferably been constructed from the start byassembling the different components, for instance according to patentapplication EP 0 919 406 by the same Applicant.

[0059] The lower cheek 6 and upper cheek 7 are respectively fastenedabove a base portion 9 of the containment structure 3, and below aclosure portion 10 of the containment portion itself. The sectors 8 arein turn engaged inside an annular portion 11 of the containmentstructure 3.

[0060] In a preferential embodiment of the invention, the curing mould 2is subdivided into an upper portion 2 a and a lower portion 2 b able tobe mutually approached to match substantially according to an equatorialmedian plane X-X of the moulding and curing cavity 4 and, hence, of thetire 5 undergoing work.

[0061] For this purpose, each circumferential sector 8 presents an upperportion 8 a and a lower portion 8 b able to be coupled in a condition ofmutual contact on a median plane, preferably on the equatorial planeX-X.

[0062] The annular portion 11 of the containment structure 3 is in turnsubdivided in an upper semi-part 11 a and a lower semi-part 11 b,presenting respective upper 12 a, and lower 12 b, cone frustum shapedinner surfaces, symmetrically opposite and diverging towards theequatorial plane X-X. The upper semi-part 11 a of the annular portion 11forms, together with the closure portion 10, an upper containmentportion 3 a of the containment structure 3, whereas the lower semi-part11 b of the annular portion 11 defines, together with the base portion9, a lower containment structure 3 b of the containment structureitself.

[0063] The upper 3 a and lower 3 b containment portions are axiallymovable relative to each other along the geometric axis Y-Y between aclosed condition wherein they match according to a diametrical plane,for instance as shown in FIG. 1, and an open condition wherein they aremutually removed, for instance as shown in FIG. 4, to allow theoperations of loading and removing the tire 5 from the moulding andcuring cavity 4. For this purpose it can for example be provided for theupper containment portion 3 a to be operatively engageable by a suitablelifting apparatus not shown herein as it is not relevant for thepurposes of the invention and achievable in any manner convenient to theperson versed in the art, for instance as described in patent EP0,459,375.

[0064] The illustrated embodiment also provides for the upper and lowercontainment portions 3 a and 3 b to be removably fastened relative toeach other in the closed condition by means of an annular bayonetclosure organ 13 operating on circumferential flanges 13 a provided incorrespondence with junction edges between the upper and lowercontainment portions themselves.

[0065] The presence of the annular bayonet closure organ 13 allows tomaintain the mould 2 in closed conditions during the tire curing cycleand further allows, if necessary, to remove the entire device 1 from asupport base 14, after disengaging removable coupling means 14 aoperating on the lower containment portion 3 b.

[0066] Each of the upper and lower portions 8 a and 8 b of the sectors 8is slidingly guided, in any manner convenient for the person versed inthe art, according to a generatrix of the respective upper interior conefrustum shaped surface 12 a, or lower interior cone frustum shapedsurface 12 b. The mobility of the upper portions 8 a and lower portions8 b of the sectors 8 along the interior cone frustum shaped surfaces 12a, 12 b is such that, following the mutual axial actuation of the upperand lower containment portions 3 a and 3 b, the upper and lower portionsof the sectors themselves are subject to translating between a closedposition wherein they are mutually approached and matching in thecircumferential direction to define the moulding and curing cavity 4,and an open condition wherein they are mutually removed both in theaxial direction and radially to the geometric axis Y-Y, to allow theinsertion and removal of the tire 5.

[0067] In accordance with the present invention, each of the sectors 8comprises essentially a support body 15 operatively engaged in thecontainment structure 3 and bearing a plurality of moulding dies 16,preferably from one to four, each of which extends according to at leasta corresponding “pitch” of the tread design to be achieved on the tire5, preferably a multiple of said pitch .

[0068] For purposes of the present description, the term “pitch” means acircumferential portion of the tread band 5 b of the tire 5, comprisinga portion of tread design which repeats circumferentially identical toitself, for instance delimited by the distances between the centres oftwo consecutive homologous transverse grooves concurring in thedefinition of the tread design.

[0069] Advantageously, each support body 15 is subdivided into an upperportion 15 a and a lower portion 15 b slidingly engaged respectively tothe upper interior cone frustum shaped surface 12 a and to the lowerinterior cone frustum shaped surface 12 b of the upper and lowercontainment portions 3 a and 3 b. The upper portion 15 and lower portion15 b of each support body 15 are further guided in a direction radial tothe geometric axis Y-Y respectively by means of an upper sliding guide20 a and a lower sliding guide 19 a positioned peripherally relative tothe upper cheek 6 and lower cheek 7.

[0070] Each moulding die 16 is in turn subdivided into an upper portion16 a and a lower portion 16 b respectively engaged to the upper portion15 a and lower portion 15 b of the corresponding support body 15.

[0071] In a preferential embodiment, to each support body 15 isassociated a pair of moulding dies 16. In this circumstance, when a tire5 is manufactured whose tread design presents, for instance, sixty-fourpitches, thirty-two support bodies 15 shall be provided, each subdividedinto a respective upper portion 15 and lower portion 15 b.

[0072] For the purposes of the present invention, the number of supportbodies 15 can, in any case, be equal or corresponding to a sub-multipleof the number of dies 16 and, hence, of the circumferential pitchescomprised in the tread design.

[0073] Each die 16, and more specifically each of the upper portions 16a and lower portions 16 b composing it, is preferably engaged to therespective upper portion 15 a and lower portion 15 b of the support body15 with the possibility of sliding in circumferential direction. Forthis purpose, in dies 16, terminal projections 34 can be provided,slidingly guided in respective undercuts presented by the base body 15,all for instance as described in patent EP 0 451 832.

[0074] A FIG. 6 clearly shows, when the curing mould is in openconditions, and in any case when the sectors 8 are radially removed fromthe geometric axis Y, each of the moulding dies 16 is distanced relativeto the circumferentially adjacent die according to a lesser measure thanthe distance between two circumferentially contiguous support bodies 15.More in particular, it is provided for the distance measurable betweentwo circumferentially contiguous support bodies 15 to be at least equalto the distance measurable on average between two contiguous dies 16,multiplied times the number of dies associated to each support body 15.In this way, one has the certainty that when the sectors 8 are radiallyapproached in the closed condition, each moulding die 16 perfectlymatches the circumferentially adjacent dies without any chance that apremature interference between the circumferentially contiguous supportbodies 15 may prevent the correct closure of the mould 2.

[0075] The presence of a number of dies 16 corresponding to the numberof pitches comprising the tread design and movable in a mutuallyindependent manner in the direction of circumferential development,assures that when the mould 2 is closed each matrix 16 penetrates thetread band 5 b of the tire 5 according to a direction perfectly radialto the geometric axis Y-Y. In this way it is certain that no anomalousstresses and/of deformations are imparted to the raw elastomericmaterial constituting the tread band 5 b, as would instead be the casewith the use of traditional moulds with eight or sixteen dies, ofrelatively high circumferential extension. Moulds of this kind cannotconfer a perfectly radial actuation trajectory to all parts destined toform the tread band, causing physical and structural inconsistencies inthe finished tire which translate into performance shortfalls by thetire. In particular, one of the most significant drawbacks isconstituted by the characteristic rolling noisiness of the tire,identified by persons versed in the art with the definition of “eighthharmonic”.

[0076] It should further be noted that the subdivision of the sectors 8of the mould 2 into an upper portion 8 a and a lower portion 8 b allowsconsiderably to limit the radial excursion necessary to the sectorsthemselves to allow the introduction and removal of the tire 5. Inpractice, the radial excursion of the sectors 8, and more in particularof each of their portions 8 a, 8 b, can advantageously be limited to theamount necessary to achieve the penetration of the ribs, present on themoulding dies 16, into the tread band 5 b according to the desireddepth.

[0077] The vulcanising unit 1 further comprises heating devices able toapply heat to the tire 5, both from its interior and from its exterior,to determine its correct curing.

[0078] For the purposes of administering heat inside the tire 5, theheating devices can for instance comprise a steam injection conduit 17and a steam extraction conduit 18 communicating with the interior of thecuring bag 4 to inject, and respectively, remove steam therefrom.

[0079] For the purposes of administering heat from the exterior of thetire 5, the heating devices further comprise a lower hot table 19located adjacently to the lower cheek 6, an upper hot table 20 locatedadjacently to the upper cheek 7, and at least an annular hot table 21 a,21 b positioned around the circumferential development of the mouldingand curing cavity 4, concentrically to the geometric axis Y-Y.

[0080] The lower hot table 19 and the upper hot table 20 are axiallymovable in the respective lower and upper containment portions 3 b and 3a to determine the radial removal of the lower portions 8 b and upperportions 8 a of the sectors 8 following the mutual axial removal of theupper and lower containment portions 3 a and 3 b. For this purpose thelower hot table 19, peripherally bearing the aforesaid lower slidingguides 19 a, is constantly maintained against the lower cheek 6 by meansof lower thrust springs 22 or equivalent elastic means operating betweenthe lower cheek itself and the base portion 9 of the containmentstructure 3. Similarly, the upper hot table 20, peripherally bearing theaforesaid upper sliding guides 20 a, is constantly maintained againstthe upper cheek 7 by means of upper thrust springs 23 or equivalentelastic means operating between the hot table itself and the closureportion 10 of the containment structure 3.

[0081] The annular hot table 21 a, 21 b is in turn preferably integratedin the structure of the annular portion 11 of the containment structure3, and is essentially defined by a lower annular cavity 21 a and anupper annular cavity 21 b obtained respectively in the upper semi-part11 a and in the lower semi-part 11 b of the annular portion itself.

[0082] The aforementioned heating devices further comprise steamsupplying means routed into the lower hot table 19, upper hot table 20and circumferential hot table 21 a, 21 b.

[0083] According to the present invention, the steam supplying means,not described in detail herein since they can be embodied in any mannerconvenient to the person versed in the art, are able to supply into thelower hot table 19, and into the lower cavity 21 a of the annular hottable, steam at higher temperature than the steam supplied into theupper hot table 20 and into the upper annular cavity 21 b of the annularhot table itself.

[0084] More specifically, in a preferential embodiment the steamsupplied into the lower hot table 19 presents a temperature rangingbetween 155° C. and 165° C., whereas the temperature of the steamsupplied into the upper hot table 20 ranges between 148° C. and 158° C.

[0085] For purposes of supplying steam at differentiated temperatures,it is preferably provided for the upper annular cavity 21 b of thecircumferential hot table to be in fluid communication with the upperhot table 20, whilst the lower annular cavity 21 b of thecircumferential hot table is in fluid communication with the lower hottable 19.

[0086] Externally to the containment structure 3, and more specificallyon each of the upper semi-part 11 a and lower semi-part 11 b of theannular portion 11, a first and a second fluid-dynamic junction elements24, 25 are provided, whereto respective steam delivery pipelines (notshown), coming from the aforementioned steam supply means, can beengaged.

[0087] The steam injected into the lower annular cavity 21 a of thecircumferential hot table 21 a, 21 b is transferred into the lower hottable 19 through a first junction pipeline indicated by the dashed line26.

[0088] Similarly, the steam injected into the upper annular cavity 21 bof the circumferential hot table 21 b is transferred into the upper hottable 20 through a second junction pipeline indicated by the dashed line27.

[0089] A first and a second output junction 28, 29 allow the evacuationof the steam respectively from the lower hot table 19 and from the upperhot table 20.

[0090] It should be noted that the supply of the steam at differenttemperatures respectively for the upper portion 2 a and for the lowerportion 2 b of the mould 2 determines an unexpected homogeneity in thedelivery of heat between the different components of the mould itselfand especially to the tire 5 undergoing work.

[0091] The Applicant has become aware that an appreciable portion of theheat dissipated by the lower hot table 19, as well as by the lowerannular cavity 21 a of the circumferential hot table 21 a, 21 b istransmitted to the upper portion 2 a of the mould 2 through the naturaltendency of hot air to rise.

[0092] Moreover, the higher temperature of the steam injected into thelower portion 2 b of the mould 2 compensates for the heat dissipationfrom the lower cheek 6 and from the lower portions 8 b of the sectors 8,particularly considerable when replacing the tire 5 undergoing work,when the vulcanising unit 1 remains completely open in the absence ofthe tire itself.

[0093] After the above description, prevalently structural, theoperation of the curing device according to the present invention shallbe described below.

[0094] Simultaneously with the closure of the tire 5 undergoing workwithin the mould 1, steam is supplied into the lower hot table 19, upperhot table 20 and circumferential hot table 21 a, 21 b as describedpreviously, to determine a homogeneous administration of heat throughthe outer surfaces of the tire itself.

[0095] At the same time, steam is injected into the interior of themoulding and curing cavity 4, to provide heat also through the innersurfaces of the tire 5. Throughout the entire curing cycle, the beads 5c of the tire 5 are withheld against the internal circumferential edgesof the respective cheeks 6, 7: in the embodiment of the vulcanising unitshown in the figures, this holding action is effected by means of theupper and lower gripping means 30 and 31, both readied in operativecondition before beginning the injection of steam into the moulding andcuring cavity 4.

[0096] The injection of steam into the moulding and curing cavity 4 canbe followed, after a predetermined time, by the injection of an inertgas such as high-pressure nitrogen, to assure the perfect penetration ofthe tread band 5 b of the tire 5 by the moulding dies 16.

[0097] Once the curing cycle, which can require a time ranging between10 and 30 minutes, depending on the dimensions and structure of the tireto be cured, is complete, the inert gas and the vapours still present inthe moulding and curing cavity 4 are evacuated therefrom, and thebayonet closure organ 13 is rotated angularly to allow the opening ofthe mould 2 by the lifting of the upper portion 3 a of the containmentstructure 3.

[0098] In an initial phase of this lifting operation, as shown in FIG.2, the upper and lower thrust springs 23 and 22 cause the upper andlower hot tables 20 and 19 to move away from the respective closureportion 10 and base portion 9 of the containment structure 3, causingthe sliding of the upper portions 8 a and of the lower portions 8 b ofthe sectors 8 on the internal cone frustum shaped inner surfaces 12 a,12 b of the annular portion 11.

[0099] In this situation, the sectors 8 move radially away from the axisY-Y, causing the moulding dies 16 to disengage from the tread band 5 bof the tire 5, whilst the upper and lower portions 8 a and 9 b of thesectors themselves, by effect of the upper springs 23 and of the lowersprings 22, are maintained in mutual contact (FIG. 2) and in mutuallyopposite thrusting relationship.

[0100] Simultaneously with the initial removal phase of the upperportion 3 a of the containment structure 3, the upper gripping organ 30is brought to a resting condition to free the upper bead 5 c of the tire5, whilst the lower gripping organ 31 maintains the lower bead engagedon the lower cheek 6.

[0101] Therefore, with the further lifting of the upper portion 3 a ofthe containment structure 3, and the consequent move of the upperportion 2 a away from the lower portion 2 b of the mould 2, thedetachment of the tire 5 from the upper cheek 7 is brought about, as perFIG. 3.

[0102] Once this operation has been completed, the upper containmentstructure 3 a is lowered again until the upper portions 8 a of thesectors 8 are again brought in contact on the respective lower portions8 b, whereupon the upper gripping organ 30 is again brought in operativecondition to hold the upper bead 5 c of the tire 5 against the uppercheek 7.

[0103] The lower gripping organ 31 is in turn brought to the restingcondition by freeing the lower bead 5 c of the tire 5 in such a way thatthe tire itself is able to be detached from the lower cheek 6 andextracted from the lower portion 3 b of the containment structure 3 as aresult of the new lifting of the upper portion 3 a , as shown in FIG. 4.

[0104] The upper portion 3 a of the containment structure 3 is thereforeable to be translated laterally relative to the lower portion 3 b insuch a way that the tire 5, previously detached from the upper cheek 7,can be laid on a roller bed 33 or other suitable collection means,following the translation of the upper gripping organ 30 in the restingcondition after the lowering of the upper portion 3 a or of the uppergripping organ alone, as shown in FIG. 5

[0105] Once the cured tire is released on the roller bed 33, the device1 is ready to receive in engagement a new tire to be cured which,through any means suitable for the purpose, will be positioned coaxiallywith its own upper bead 5 c above the upper gripping organ 30. Thelatter shall subsequently be brought to the operative condition toengage the bead 5 c of the new tire 5 against the inner circumferentialborder of the upper cheek 7.

[0106] The upper portion 3 a of the containment structure 3, afterhaving been coaxially brought back above the lower containment portion 3b, shall be lowered thereon, to determine the closure of the new tire 5in the mould 2.

[0107] The present invention achieves important advantages.

[0108] The provision of steam at differentiated temperaturesrespectively for heating the upper and lower part of the mould allows anoptimal distribution of the heat administered to the tire whichadvantageously brings about a high degree of uniformity of the curedtire and of its operating performance.

[0109] The method according to the invention originates from theintuition that the lower hot table must be supplied with steam at adetermined temperature corresponding with that necessary for a correctcuring of the lower sidewall and that the upper hot table must besupplied with steam at a lower temperature according to a predeterminedquantity to that the difference between the two temperatures issubstantially compensated for by the inflow of heat transferred andemitted upwards by the lower part of the vulcanising unit.

[0110] Advantageously the difference between the temperatures at whichthe steam is supplied to the cheeks of the mould translates into auniformity of characteristics and performance for the two sidewalls ofthe tire.

[0111] Moreover, very favourably, the higher temperature of the steaminjected into the lower portion 2 b of the mould 2 compensates for thedissipation of heat from the lower cheek 6 and from the lower portions 8b of the sectors 8, particularly considerable when replacing the tire 5undergoing work, when the device 1 remains completely open in theabsence of the tire itself.

[0112] By way of non limiting indication, it is specified that theApplicant has found particularly advantageous the modification of thetemperature of the fluids of the curing cycle, normally carried out, asindicated below, in accordance with the invention and with reference toa curing press equipped with curing bag, for curing tires ranging insize from 185/65R15 and 254/40R18. TABLE 1 Temperatures for Temperaturesfor Invention Devices Prior Art Method (° C.) Method (° C.) Curing Bag200 200 Upper Annular Hot 180 156 Table Lower Annular Hot 180 159 TableLower Cheek Hot Table 160 159 Upper Cheek Hot Table 160 156 CycleDuration (min.) 14′-25′ 10′-19′ Energy Consumption 2100  1500  (kcal/kg)

[0113] The results of bench and road tests confirm, through the highdegree of homogeneity and uniformity of the structural and behaviouralcharacteristics of the tires, the excellent distribution of the heatadministered to the tire achieved with the provision of steam atdifferentiated temperatures respectively for heating the upper and thelower part of the mould 2.

[0114] In particular, the homogeneity of the distribution of heat on theopposite sidewalls of the tire is greatly improved, overcoming thelimitations of the state of the art where, in spite of the contrivancesadopted to try to obtain a temperature of the curing fluid that isexactly identical between the lower hot table and the upper hot table,it was always difficult to obtain the same degree of curing on the twosidewalls of the tire: the one situated superiorly always had a tendencyto be over-cured relative to the sidewall situated inferiorly.

[0115] It should further be noted that, advantageously, the lowertemperature of the steam supplied into the two tables translates intoless energy consumption per tire and per vulcanising unit, quiteappreciable in relation to the number of curing devices simultaneouslyin use.

[0116] The optimisation of the distribution of the head transferredthrough the mould allows to achieve considerable improvements in termsof caloric expenditure, thanks to the additional constructivepeculiarities of the subject device. It should be noted, in fact, thatthe construction of the mould 2 and of the containment structure 3 intwo semi-parts subdivided on the equatorial plane allows to minimise, asstated, the radial excursion that the sectors 8 must perform during theopening phase to allow the removal and reintroduction of the tiresundergoing work.

[0117] In this situation the sectors remain very close to each othereven when the device is fully open, thereby avoiding excessive heatlosses, which do instead take place in the moulds constructed accordingto the prior art, wherein the sectors are obtained in a single piece andconnected to a sole sector-bearing ring so that they are considerablydistanced from each other when the vulcanising unit is open.

[0118] The constructive features adopted in the realisation of thesectors further confer a reduced thermal inertia to the sectorsthemselves, which reduced thermal inertia is also allowed by thecontainment of heat dissipation during the opening phase. Exploitingthis reduced thermal inertia in an original and advantageous manner, theinvention proposes to supply the portions of the annular hot table withsteam at the same temperature (with the same steam) as the steaminjected into the upper and lower hot tables, thereby eliminating theneed to provide an additional supply of steam at different temperaturesfor the annular hot table.

1. A method for curing a tire entailing the use of a curing mould (2)presenting a moulding and curing cavity (4) able to receive a tireundergoing work (5), a lower hot table (19) and an upper hot table (20)axially opposite and able to operate on respective sidewalls (5 a) ofthe tire (5) and at least an annular hot table (21 a, 21 b) positionedaround the circumferential development of the moulding and curing cavity(4), comprising the following phases: closing a tire to be cured (5) inthe moulding and curing cavity (4); heating the lower hot table (19),upper hot table (20) and annular hot table (21 a, 21 b) to transmit heatto the tire (5), providing different quantities of heat to said hottables during said heating phase, in order to cure the tirehomogeneously, characterised in that said heating phase is conductedsupplying the lower hot table (19) with a greater quantity of heat thanthe heat supplied to upper hot table (20).
 2. A method as claimed inclaim 1, wherein the heating of the annular hot table (21 a, 21 b) isconducted supplying its lower portion (21 a) with a greater quantity ofheat than the heat supplied to its upper portion (21 b).
 3. A method asclaimed in claim 1, wherein the heating of the hot tables (19, 20, 21 a,21 b) is conducted by supplying a heating fluid to the tablesthemselves, the fluid supplied to the lower hot table (19) presenting ahigher temperature than the temperature of the fluid supplied to theupper hot table (20).
 4. A method as claimed in claim 1, wherein theheating fluid supplied to a lower portion (21 a) of the annular hottable presents higher temperature than the temperature of the heatingfluid supplied to an upper portion (21 b) of the annular hot tableitself.
 5. A method as claimed in claim 4, wherein the fluid supplied tothe lower hot table (19) is supplied also to the lower portion (21 a) ofthe annular hot table.
 6. A method as claimed in claim 4, wherein thefluid supplied to the upper hot table (20) is supplied also to the upperportion (21 b) of the annular hot table.
 7. A method as claimed in claim3, wherein the fluid supplied to the lower hot table (19) comprisessaturated dry steam at a temperature ranging between 155° C. and 165° C.8. A method as claimed in claim 3, wherein the fluid supplied to theupper hot table (20) comprises saturated dry steam at a temperatureranging between 148° C. and 158° C.
 9. A device for curing tires forwheels of vehicles comprising. a curing mould (2) defining a mouldingand curing cavity (4) able to receive a tire undergoing work (5); atleast a lower hot table (19) positioned adjacently to a lower cheek (6)of said curing mould (2); at least an upper hot table (20) positionedadjacently to an upper cheek (7) of said curing mould (2); at least anannular hot table (21 a, 21 b) positioned around the circumferentialdevelopment of the moulding and curing cavity (4) positioned adjacentlyto a plurality of moulding dies of said curing mould (2); devices (24,25, 26, 27, 28, 29) for supplying heating fluid into said hot tables(19, 20, 21); supplying devices for supplying said heating fluid todifferentiated portions of said hot tables, in mutually independentfashion, until curing both sidewalls of the tire homogeneously,characterised in that said means for supplying fluid supply the lowerhot table (19) with fluid at a higher temperature than the temperatureof the fluid supplied to the upper hot table (20).
 10. A device asclaimed in claim 9, wherein the annular hot table (21 a, 21 b) isdivided into at least a lower cavity (21 a) and at least an upper cavity(21 b) following a plane that is diametrical relative to the mouldingand curing cavity (4).
 11. A device as claimed in claim 10, wherein saidfluid supplying means (24, 25, 26, 27, 28, 29) supply the lower cavity(21 a) of the annular hot table with fluid at a higher temperature thanthe fluid supplied to the upper cavity (21 b) of said annular hot table.12. A device as claimed in claim 10, wherein the lower cavity (21 b) ofthe annular hot table is in fluid communication with the lower hot table(19).
 13. A device as claimed in claim 10, wherein the upper cavity (21b) of the annular hot table is in fluid communication with the upper hottable (20).
 14. A device as claimed in claim 9, wherein said fluidsupplying means (17, 18, 24, 25, 26, 27, 28, 29) further comprise atleast an injection conduit (17) discharging into the interior of themoulding and curing cavity (4) and at least an extraction conduit (18)originating from the moulding and curing cavity itself.
 15. A device asclaimed in claim 10, wherein said lower cavity (21 a) and said uppercavity (21 b) of the annular hot table (21) are respectively obtained inan upper containment portion (3 b) and in a lower containment portion (3a) of a containment structure (3), said containment portions beingmutually movable between a closed condition wherein they are in mutualcontact and an open condition wherein they are axially distanced.
 16. Adevice for curing tires for wheels of vehicles, in particular as claimedin claim 9, wherein said mould (2) comprises a plurality of lower radialsectors (8 a) and a plurality of upper radial sectors (8 b) respectivelyengaged in said lower containment portion (3 b) and upper containmentportion (3 a), circumferentially distributed about a geometric axis(Y-Y) of the moulding and curing cavity (4), each of said sectors (8 a,8 b) comprising a support body (15) slidingly engaged in thecorresponding containment portion (3 a, 3 b) to be selectivelydisplaced, simultaneously with the mutual axial actuation of saidcontainment portions, between a closed condition wherein said sectorsare mutually approached and matching to define the moulding and curingcavity (4), and an open condition wherein the sectors of the sameplurality are radially removed relative to said geometric axis (Y-Y),circumferentially distanced one from the other, and axially distancedrelative to the sectors of the opposite plurality, each of said sectors(8 a, 8 b) further comprising at least a moulding die (16) removablyengaged to the support body (15).
 17. A device as claimed in claim 16,wherein to each support body (15) are engaged at least two of saidmoulding dies (16) slidingly guided on the support body itself andmutually movable according to a circumferential direction relative tothe moulding and curing cavity (4).
 18. A device as claimed in claim 16,wherein each of said moulding dies (16) presents a circumferentialextension corresponding to a pitch of a tread design to be defined onthe tire undergoing work (5).
 19. A device as claimed in claim 16,wherein in the closed condition said pluralities of lower sectors (8 b)and upper sectors (8 a) mutually match according to a median equatorialplane of the moulding and curing cavity (4).
 20. A device as claimed inclaim 19, wherein to each support body (15) are engaged at least two ofsaid moulding dies (16) slidingly guided on the support body itself andmutually movable according to a circumferential direction relative tothe moulding and curing cavity (4).
 21. A device as claimed in claim 19,wherein each of said moulding dies (16) presents a circumferentialextension corresponding to a pitch of a tread design to be defined onthe tire undergoing work (5).
 22. A device as claimed in claim 19,wherein in the closed condition said pluralities of lower sectors (8 b)and upper sectors (8 a) mutually match according to a median equatorialplane of the moulding and curing cavity (4).